This invention relates to a method for the preparation of tin-containing vanadium-antimony oxide catalysts useful for the catalytic ammoxidation of C3 to C5 paraffins or olefins, more specifically for the preparation of catalysts for the ammoxidation of propane or isobutane or propylene or isobutylene to its corresponding xcex1,xcex2-unsaturated mononitrile, acrylonitrile or methacrylonitrile. In addition, the catalyst may be used in the ammoxidation of methylpyridine, m-xylene or the oxidation of o-xylene to cyanopyridine, isophthalonitrile or phthalic anhydride, respectively.
More specifically, the invention relates to the use of a SnO2.xH2O wherein xxe2x89xa70 dispersed in a solution of a tetraalkyl ammonium hydroxide as the reagent for tin in the preparation of catalysts containing vanadium and antimony and tin in oxide form. These types of catalysts are disclosed for instance in U.S. Pat. Nos. 3,681,421, 4,788,317, 5,008,427 and in British specifications 1,336,135 and 1,336,136, published in November 1973.
Not all sources of tin are equally effective as promoters in vanadium-antimony oxide catalysts for the oxidation and ammoxidation of saturated C3 and C4 alkanes, particularly ammoxidation. In facts U.S. Pat. No. 5,214,016 and EPO 691306-A1 teach that the source of tin promoter is critical to the performance characteristics of the finished catalyst. It is believed that the tin should be present in very finely divided form in the precursors of such catalysts in order for the tin to be fully reactive when the solid state reaction takes place upon calcination of the catalyst precursor mixture. Tin oxide sol is a suitable source in making catalysts of the present invention; see U.S. Pat. No. 5,008,427. However, ground tin oxide or tin oxide made by if reacting tin metal with nitric acid are decidedly less effective sources in catalyst preparation. While current commercially available tin oxide sol is effective, it has a serious disadvantage because it is a very expensive source.
It is an object of the present invention to provide a method of making a superior oxidation (particularly ammoxidation) catalyst while avoiding the use of current commercially available tin oxide sols.
It is another object of the invention to make such a catalyst at a fraction of the expense with respect to the tin component as compared to using current commercially available tin oxide sol as the source of tin in the catalyst precursor.
Other objects, as well as aspects, features and advantages, of the invention will become apparent from a study of the specification including the specific examples.
The foregoing and other objects are accomplished by the present invention according to which there is provided a method of making a catalyst containing vanadium, antimony and tin in the oxide state which comprises making an aqueous slurry of a mixture of source batch materials comprising compounds of the elements to be included in the final catalyst, followed by drying and calcining the mixture to form an active catalyst, wherein the source batch material for the tin is a solution which comprises SnO2.xH2O wherein xxe2x89xa70 dispersed in tetraalkyl ammonium hydroxide wherein the tetraalkyl ammonium hydroxide is defined by the following formula:
xe2x80x83(CnH2n+1)4NOH
wherein 5xe2x89xa7nxe2x89xa71.
Preferably, tetramethyl ammonium hydroxide is utilized in the practice of the invention.
The catalyst can be made from any suitable organic or inorganic precursor compounds of V and Sb, and compounds used to introduce other optional elements into the final catalyst after calcination, as is well known in the art, such as the salts, oxides, hydroxides or metallo-organic compounds of such elements, with the tin being introduced to the batch of raw materials for preparing such catalysts in the form of a solution of SnO2.xH2O dispersed in tetraalkyl ammonium hydroxide as previously disclosed herein. The batch mixture of precursor materials is heated and calcined in a known manner until the final catalyst results. Examples of such raw source batch materials are of course shown in the specific working examples herein.
Particularly effective procedures for the manufacture of the catalyst are set forth in U.S. Pat. Nos. 4,784,979, 4,879,264, 3,860,534 and 5,094,989, herein incorporated by reference. In addition, the catalyst may optionally be treated by one or more of the methods disclosed in U.S. Pat. Nos. 5,432,141 and 5,498,588, also herein incorporated by reference.
In making the catalysts of the present invention, the upper calcining temperature is usually at least 500xc2x0 C., but for ammoxidation of paraffins this temperature is preferably over 750xc2x0 C., most often at least 780xc2x0 C.
The catalyst may be unsupported or supported on a suitable carrier. Preferably the catalyst is supported on a carrier such as silica, alumina, silica alumina, zirconia or mixtures thereof.
A preferred method of the invention is to make catalysts having the elements and the proportions indicated by the empirical formula:
VSbmAaDdOx
where
A is one or more Ti, Sn, where Sn is always present
D is one or more Li, Mg, Ca, Sr, Ba, Co, Fe, Cr, Ga, Ni, Zn, Ge, Nb, Zr, Mo, W, Cu, Te, Ta, Se, Bi, Ce, In, As, B, Al and Mn wherein
m is 0.5 to 10
a is greater than zero to 10
d is zero to 10
x is determined by the oxidation state of the cations present,
which comprises making an aqueous slurry of a mixture of source batch materials comprising compounds of said elements to be included in the final catalyst, followed by drying and heat calcining the mixture to an active catalyst, wherein the source batch material for the tin is a solution which comprises SnO2.xH2O wherein xxe2x89xa70 dispersed in tetraalkyl ammonium hydroxide wherein the tetraalkyl ammonium hydroxide is defined by the following formula:
(CnH2n+1)4NOH
wherein 5xe2x89xa7nxe2x89xa71,
drying said slurry and calcining the mixture to an upper calcination temperature of at least 780xc2x0 C. The upper calcination temperature can be up to 1200xc2x0 C., but is most often not over 1050xc2x0 C.
In another aspect of the present invention, there is provided a process for making an xcex1,xcex2-unsaturated mononitrile selected from acrylonitrile and methacrylonitrile, by the catalytic reaction in the vapor phase of a paraffin selected from propane and isobutane with molecular oxygen and ammonia and optionally a gaseous diluent, by catalytic contact of the foregoing reactants in a reaction zone with a catalyst, the feed to said reaction zone containing a mole ratio of said paraffin to NH3 in the range from 2.5 to 16 (preferably 4 to 12; especially preferred being 5 to 11) and a mole ratio of said paraffin to O2 in the range from 1 to 10 (preferably 2 to 9, especially preferred being 3 to 9), said catalyst having the empirical composition recited in the last previous paragraph, said catalyst having been made by the method of the last previous paragraph.
The catalyst may also be used in the ammoxidation of methylpyridine and m-xylene to cyanopyridine and isophthalonitrile or the oxidation of o-xylene to phthalic anhydride. The mole ratios of NH3 to methylpyridine and O2 to methylpyridine are 1 to 5 and 1 to 10, respectively. The mole ratios of NH3 to m-xylene and O2 to m-xylene are 1 to 5 and 1 to 10, respectively. In the phthalic anhydride reaction, the ratio of O2 to o-xylene may range from 1 to 10.
The catalyst prepared by the process of the present invention may also be utilized in the ammoxidation of propylene or isobutene with ammonia and oxygen to produce acrylonitrile or methacrylonitrile. The mole ratio of NH3 to olefin may range from about 1 to 5 and the mole ratio of O2 to olefin may range from 1 to 10 in this reaction under conventional temperatures and conditions well known in the art.